Controlled polyamide filament stretching process

ABSTRACT

HIGH DRAW RATIOS CAN BE ACHIEVED TO YIELD HIGHSTRENGTH POLYAMIDE HOSIERY YARN WHICH EXHIBITS UNIFORM LUSTER BY MAINTAINING THE RATIO   AT LESS THAN 1.02 GRAMS PER DENIER-CM T1 IS TENSION ON A FILAMENT APPROACHING THE DRAW ZONE; T2 IS THE TENSION ON A FILAMENT RECEDING FROM THE DRAW ZONE; D IS THE DRAWN DENIER OF THE FILAMENT AND D IS THE DIAMETER OF THE DRAW PIN OR SNUBBING ELEMENT IN CM.

Jan. 26, 1971 F. GOPEZ, JR I 3,553,767

' CONTROLLED POLYAMIDE FILAMENT STRETCHING PROCESS I Filed Nov. 19, 1968INVENTOR F2 0901/00 cop/52, JR

United States Patent O U.S. Cl. 264290 2 Claims ABSTRACT OF THEDISCLOSURE High draw ratios can be achieved to yield highstrengthpolyamide hosiery yarn which exhibits uniform luster by maintaining theratio at less than 1.02 grams per denier-cm. T is the tension on afilament approaching the draw zone; T is the tension on a filamentreceding from the draw zone; D is the drawn denier of the filament and dis the diameter of the draw pin or snubbing element in cm.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the production of nylon filaments, and more particularly, toan improved process for the production of such filaments for use inladies hosiery.

Description of the prior art In the manufacture of ladies nylon hosiery,monofilaments are commonly used as the leg yarn with rnultifilamentyarns used in the welt, heel and toe. In the United States 15 monofilsprevail, while in Europe higher deniers such as 20 denier are morecommonly used. Although nylon filaments dominate the field of ladieshosiery in view of their relatively high strength and other desirablequalities, the use of relatively low denier yarns needed to providesheer hose which the market demands results in a lower'hose wear lifethan is desirable.

Increased hose durability may be achieved by increasing the strength ofthe filaments. This may be accomplished by increasing the molecularweight of the polymer and the draw ratio employed in processing thefilaments However, when high draw ratios are used in conventional pindrawing of nylon filaments of this type, the hose prepared from thefilaments tend to have a streaky appearance which is apparently due tooccasional changes in luster, ie, the manner in which the filamentsreflect light. These luster streaks are highly undesirable and must beeliminated in order to achieve a commercially acceptable hosiery yarn.In addition, the use of high draw ratios leads to a high incidence ofbroken filaments such that the process is commercially unacceptable.

SUMMARY OF THE INVENTION High draw ratios can be achieved withoutdeleterious eifect on a polyamide filament by drawing an undrawnPatented Jan. 26, 1971 polyamide filament by passing it from a feederroll at a tension, T to and around an unheated snu bbing element ofsubstantially circular cross section having a diameter, d, withdrawingthe filament at tension, T from the snub- 5 bing element with a drawroll, heating the filament between the snubbing element and draw roll toefiect additional draw. This process must be carried out under thefollowing conditions: the drawn denier, D, of the filament must be inthe range of from 10 to 30; the absolute draw ratio must be at least5.4; and the ratio 'must be no greater than 1.02 grams per denier-cm.Preferably the diameter of the snubbing element is from 2.5 to 5centimeters and the relative viscosity of the undrawn polyamide filamentis at least 50. Under normal process conditions the filament is heatedat a temperature in the range of from 170 C. to 230 C.

BRIEF DESCRIPTION OF THE DRAWING The figure is a simplified schematicrepresentation of the apparatus by which the process of this inventioncan be practiced.

DEFINITIONS The expression relative viscosity as used herein signifiesthe ratio of flow time in a viscometer of a polymer solution relative tothe flow time of the solvent by itself. Measurements of relativeviscosity are made with 5.5 gms. of polyamide in 50 ml. of formic acidat 25 C.

Machine draw ratio, as referred to herein, is calculated by dividing thespeed of the yarn leaving the draw zone by the entering speed. Wherefeed and draw rolls are employed, the yarn speed is assumed to be thesame as the surface speed of the rolls.

Yarn birefringence, as employed herein, refers to the birefringence ofthe extruded and quenched, but undrawn, filament. Birefringence is ameasure of the orientation of the polymer chains relative to the fiberaxis. It is determined from observation of the filament between crossedplane-polarizing elements, e.g., Nicol prisms, using a Soleilcompensator for accuracy. The method is described in detail by Heyn inTextile Research Journal 22, 5-13 (1952).

Since the undrawn yarn is oriented to some degree, and this may varyconsiderably depending on polymer viscosity and extrusion conditions,the orientation of the drawn yarn is not accurately reflected by themachine draw ratio. Hence, it is desirable to use an absolute draw ratiowhich takes into account orientation prior to drawing. It has been foundthat an absolute draw ratio calculated from the following empiricalequation, satisfactorily reflects the contribution of the undrawnfilament orientation to the total orientation existing in the drawnyarn:

Absolute Draw Ratio: (1+22.2B 284B R where B is undrawn yarnbirefringence and R is machine draw ratio.

DESCRIPTION OF PREFERRED EMBODIMENTS Nylon hosiery yarn is prepared byextruding and quenching molten polyamide to form monofilaments. For

purposes of this invention the monofilaments at this stage shouldpreferably have a relativeviscosity of'at least 50 and a deniersuflicient to yield a final drawn denier in the range of to 30. Thenewly formed filaments are usually wound into a package and transportedto a drawing apparatus.

Referring to the figure, the undrawn nylon filament 4 is supplied fromyarn package 2. The yarn need not be taken from a package as shown, butmay be taken directly from a spinning machine to continuously processthe yarn. The yarn 4 is passed from the package through guide 6 to afeed roll 8, about which the yarn is wrapped. The feed roll ispositively driven and may be associated with a nip roll, if desired.From the feed roll the yarn is advanced to and around draw pin orsnubbing element 10. The yarn is pulled away from or withdrawn from thesnubbing element across a curved heated plate 12 by driven draw roll 14and its associated separator roll 16. The yarn can be wrapped arounddraw pin 10 one and one-half times or any other amount necessary toeffectuate drawing of the filament at the snubbing element. The plate 12can be heated by any conventional means. As the yarn is heated when itpasses over the plate, additional drawing is accomplished, The relativeperipheral speeds of the draw roll 14 and the feed roll 8 determine themechanical draw ratio of the filament. The drawn yarn is taken from thedraw roll 14, passed through guides 18 and 22, and wound on bobbin 24.

The tension on the filament prior to and after contact with the snubbingelement is determined by a number of factors, including the peripheralspeeds of the draw roll 14, the feed roll 8, the denier of the filamentand the friction between the snubbing element 10 and the filament. Thetension between the feed roll and snubbing element is represented in thefigure by T the tension between the draw roll and snubbing element isrepresented by T The snubbing element friction is proportional to thediameter, d, of the element.

The filament is heated during the drawing process by passing it from thesnubbing element over a curved hot plate between the snubbing elementand draw roll whereby the filament is subjected to additional drawingwithout substantial snubbing action which would tend to distort thefilament cross-section.

Excess transverse pressure on the filaments should be avoided both onthe snubbing element in the first draw zone and in the second draw zoneto prevent fabric luster streaks which are believed to result fromdistortion of the cross-section. Excessive pressure in the first drawzone may be avoided by correct sizing of the drawing element in relationto the tension imposed on the filament in this zone. However, in orderto provide adequate snubbing action, diameters greater than 5 cm. shouldbe avoided and the minimum diameter should be at least about 2.5 cm. toavoid the necessity for low tensions which are not practical Where ahigh draw ratio is desired. The tension, T on the filament leaving thefirst draw zone is regulated primarily by the temperature imposed in thesecond draw zone and to a lesser extent by the friction between thefilament and the heating element in this zone.

It is especially important that excessive transverse pressures on thefilament be avoided in the heated draw zone. Consequently, substantialsnubbing of the filaments should be avoided. While heating in this zonemay be varied to suit the polymer used to prepare the filaments,temperatures in the range of 170 C. to 230 C. are usually required forsatisfactory results. The heating and frictional contact with anysurface in the heating zone should be adjusted so that the drawing inthe heated zone is substantially less than that in the unheated drawzone.

Where it is necessary to reduce the shrinkage in aqueous solution of thefilaments, as may be required with certain polyamides and particularlywith copolyamides, this may be accomplished by passing the filamentsthrough a heated zone under low tension. Filaments may be heated atcon.- stant length or retraction of the filaments may be permitted, thelatter procedure being preferred where a copolymer filament having a lowshrinkage tension is desired. In some cases it may be desirable toemploy heating at constant length followed by further heating underconditions which permit retraction of the filament. With mostcopolyamides, a retraction in the range of 11-18% will provesatisfactory. I

It is highly desirable that the relative viscosity of the extrudedfilament be at least 50 in order to achieve high strength, andconsequently a high level of durability in hose. I

EXAMPLES The examples are intended as illustrative of preferred modes ofcarrying out the process of this invention. They are not intended to bein any way delimitative 0f the inventive concept.

EXAMPLE I A copolyamide flake is prepared from hexamethylenediammoniumadipate and epsilon-caprolactam following the general procedure ofExample I of U. S. Pat. 3,322,- 721. The copolymer contains 6-6 polymerunits and 15%' 6 polymer units. The relative viscosity of the flake is44. The flake is heated in a nitrogen atmosphere to remove additionalwater, thus increasing the relative viscosity, as measured on theextruded filaments, to the level shown in Table I. The flake is meltedin a screw melter and extruded to form 15 denier (drawn denier) monofil.A heated baflie of 17.8 cm. depth is placed around the spinneret toreduce the quenching rate near the spinneret, and the spinneret isblanketed with stream at 290 C. The filament is then quenched with crossflow air, passed over a finish roll where a lubricating finish isapplied, and wound into a package. The filament is subsequently unwoundfrom the package, passed around a feed roll, then around an unheateddraw pin for 1 /2 wraps, then directly over a hot plate of 3 in. lengthto a draw roll rotating at a peripheral speed of 771 meters/ min. Thedraw roll assembly consists of a stepped roll,

the larger diameter portion of which acts as the draw.

roll, a separator roll and a heating element mountedbetween the steppedroll and separator roll to contact the yarn for a distance of about 4in. as it passes to and from the separator roll. The yarn is given 5-12passes around the draw roll portion of the stepped roll and theassociated separator roll, and is then passed to the smaller diameterportion of the stepped roll. where it is given 5-8 passes around thisroll and the separator roll, the number of passes being adjusted to givethe desired yarn shrinkage. The difference in the diameters.

of the two portions of the roll is sufficient to permit the yarn toretract 13%. The yarn, after drawing, is thus subjected to constantlength heat treatment and then per mitted to retract 13% under theinfluence of heat. The filament is then wound into a package in theconventional manner. The above process is run under various conditionsof draw pin diameters, hot plate temperature and draw ratio, as shown inTable I below. For comparison,

samples of filaments, it is found that those filaments havmg distortedcross-sections produce hose with luster streaks, while those with round,undistorted filaments do not.

In all cases where a hot plate was employed, the draw ratio in theheated zone was substantially less than the draw ratio in the unheatedzone.

TABLE I Undrawn yarn Draw ratio Hot Draw pin Plate Tz-T1, denierFilament Relat ve Birefrln- Diameter, Temp., Xdiameters cross- Tenacity,vlscosities gence Mach ne Absolute m. C. T|,g. T2, g. Denier cm. sectiong.p.d.

0.0080 4.54 5. 2 33 15.3 1.07 Distol'ted 7.53 0.0080 4. 95 5. 91 6 5414.5 1 74 d 0. 0080 4. 95 5. 91 6 55 14. 0. 0078 5. 40 6. 43 11 50 1 14.6 0. 0046 5. 24 5. 85 1 25 14. 9

1 Estimated based on spun denier and draw ratio.

7 EXAMPLE II he in the range from 25 to 75 grams, that the absoluteFollowing the general procedure of Example I, except draw who be atleast and that the who of that no heating or relaxation of the yarnsubsequent to drawing is employed, polyhexamethylene adipamide (66 T --Tnylon) yarns having relative viscosities as shown in Table II areproduced. Process variations, results of microscopic examination of thefilament cross-sections, etc., are shown in Table II below. Draw ratiosin the heated zone were be no greater than grams P substantially lessthan in the unheated draw zone. 5? P t r of i 1 l P a 55 3" EXAMPLE HIam1 e amen as a re a we vlscosity 0 at east Starting withpolycaprolactam (6 nylon) flake having a relative viscosity of 59, an 80relative viscosity flake is produced and processed into filamentsfollowing the procedure of Example I except that no heating orrelaxation of the yarn subsequent to drawing is employed. Processvariables, results of microscopic examination of these filaments, etc.are shown in Table III below. Draw ratios in the heated zone weresubstantially less than in the unheated draw zone.

TABLE II Undrawn yarn Draw ratio Hot Draw pin Plate Tz-T1, denierFilament Relative Birefrin- Diameter, Temp., XDiameters cross- Tenacity,viscositie gence Machine Absolute em. 0. T1, g. T2,g- Denier cm. sectiong.p.d.

0. 0020 4.95 5. 3.81 175 7 29 13.0 0.442 Round 7 4 0.0039 4.67 5.10 3.81200 3 48 17.3 0.683 d0 0.0039 5.09 5.55 3.81 200 7 65 15.5 0.96 .do 7 620. 0039 5.24 5.71 3.81 200 7 72 15.0 1 14 Distorted 8 12 0.0040 5.245.72 3.81 '230 13 68 14.4 1.005 Round 9.0 0. 0040 5.40 5.90 3.81 230 1475 14.2 1.13 Distorted-.. 9.3

1 Estimate based on draw ratio vs. elongation for 63 and 53 RV yarns.

TABLE III Undraw'n yarn Draw ratio Hot Draw pin Plate Tz-T1, DenierFilament Birefrin- Diameter, Temp., X Diameter, cross- Tenacity,Relative viscosities gence Machine Absolute em. C. T1,g- T2,g- Denier0111- seetion g.p.d.

80 0.0062 4.88 5. 59 3.81 200 0 36 16.4 0. 575 Round 7.77 80 0.0062 5.175.9 3.81 200 0 42 15.7 0.705 .....d@ 8.48

STATEMENT OF UTILITY References Cited 7 The process of this inventiondelineates conditions by UNITED STATES PATENTS which filamentary nyloncan be subjected to higher draw 3 011 215 12 19 1 Alley 2 7 ratios thanheretofore could be achieved without filament 3 091 015 5 9 3 Zimmermandeformation. Draw ratios of greater than 5.4 can now be 3 303 1 9 2 19 7pitzl 264 290 achieved without crushing the filament by utilizing the 33 2 307 5 19 Ciceri et 1 264 210 process e e disclosed- 3,400,194 9/1968Boone et a1 264-210 The splnt and scope of thls invention shall only be3,414 4 12/19 3 Pitzl 2 4 0 limited by the appended claims and anyequivalents or 3,441,642 4/1969 Engelman et a1 modifications thereofwithin the purview of the art. 3,452,130 6/1969. Pitzl 264 210 What ISclalmed 3,452,131 6/1969 'Geerdes et a1. 264-290 1. A process fordrawing an undrawn polyamlde fila- 3 472 016 10/1969 Robertson mentcomprising drawing the said filament by passing it from a feeder roll ata tension, T to and around'a 65 34914l8 1/1970 Nlclta et a1 264290snubbing element of substantially circular cross-section FOREIGN PATENTShaving a diameter d, withdrawing the filament'at a tension 889,1442/1962 Great Britain 264 290 T from the said snubbing element with adraw roll, and 636,095 2/1962 Canada heating the filament between thesnubbing element and draw roll to a temperature in the range of from 170C. DONALD ARNOLD, Primary Examiner to 230 C. to eifect additional draw,with the provisos that the drawn denier D, of the filament be in therange MINTZ Asslstant Exammer of from 10 to 30, the diameter of thesnubbing element U S Cl X R d, be in the range of from 2.5 to 5 cm., thetension T be in the range of from 0 to 14 grams, the tension T 28-71.3,72.17; 264210

